This invention relates generally to the control of pressure fluctuations in a liquid medium and more particularly to an automatically controlled desurging system for decreasing pressure fluctuations in a fluid pumping system.
One of the principal applications of conventional hydraulic desurgers is the elimination of pressure fluctuations of fluid being pumped through a pipeline. Pumping systems employing a piston or positive-displacement type pump to circulate fluid through a pipeline impart surges or pressure fluctuations to the fluid on each pump stroke. Such pressure fluctuations create a hammer effect in the fluid system that can severely damage the system equipment. In the past it has been conventional practice to couple to the pump outlet a standard, gas-loaded, hydraulic desurger to reduce these fluctuations.
More recently, such a standard, gas-loaded, hydraulic desurger has been employed to reduce noise levels in the circulating drilling fluid of logging-while-drilling systems. An example of such a system is disclosed in U.S. Pat. No. 3,309,656 to John K. Godbey. In the Godbey system, drilling fluid is continuously circulated downward through the drill string and drill bit and upward through the annulus provided by the drill string and the borehole wall, primarily for the purpose of removing cuttings from the borehole. An acoustic transmitter located downhole continuously interrupts the flow of the drilling fluid, thereby generating an acoustic wave in the drilling fluid. The acoustic wave is modulated with information measured downhole by sensing apparatus, and the modulated acoustic wave is telemetered uphole through the drilling fluid to suitable recording equipment.
However, logging-while-drilling systems utilizing the circulating drilling fluid as a medium for telemetry have obvious difficulties in that any extraneous vibrations, shocks, etc., of the drilling equipment impart unwanted pressure waves or "noise" to the fluid which may seriously interfere with the acoustic signal being telemetered uphole in the drilling fluid at that time. This noise may be generally classified as either "downhole" or "uphole" noise, depending on the source of the unwanted pressure waves. Uphole noise, itself, originates from a variety of sources, the most prominent being the pumps which circulate the fluid through the drilling system. These pumps, which are of the piston, positive-displacement type, impart pressure surges or noise to the drilling fluid on each pump stroke. This noise has been reduced by coupling a conventional, gas-loaded, hydraulic desurger in the fluid flow line near the pump output as disclosed in the aforementioned patent to Godbey.